The present embodiments relate to detection of a probe position from x-ray imaging. Two-dimensional (2D) x-ray imaging (e.g. fluoroscopy) is routinely used for interventional cardiac surgery. x-ray imaging and transesophageal echocardiography (TEE) provide complementary information during the cardiac surgery. x-ray imaging is used to monitor interventional devices (e.g., catheter and TEE probe), and three-dimensional (3D) TEE is used to visualize soft tissue. To fully utilize complementary information from both modalities, the coordinate systems of the x-ray and ultrasound are registered or aligned. Detecting the 3D pose of a TEE probe from x-ray images enables the fusion of x-ray and ultrasound images. With an accurately estimated 3D pose of the TEE probe, measurements or annotations in the ultrasound image or the x-ray image can be transferred to the coordinate system of the other modality.
A challenge in 3D pose detection from single view x-ray image is the ambiguity of depth, which causes largely inaccurate estimation of the object's movement along the viewing axis of the C-arm detector of the x-ray system. Conventional methods to resolve the depth ambiguity typically involve acquiring at least two x-ray images of the TEE probe from different angles (e.g., 30 degrees apart) during the procedure or intervention. However, a bi-plane system to acquire two x-ray images simultaneously is not commonly available due to increased equipment cost, and the additional radiation dose associated with bi-plane acquisition is undesired. For a mono-plane system, once the interventional procedure starts, it is inconvenient and may be impossible to rotate the C-arm to acquire two images at different angles during the procedure because of the density of equipment in the operating room. In addition, real-time TEE probe pose estimation for dynamic fusion of ultrasound and x-ray images becomes impossible when a C-arm needs to be rotated between different angles in order to acquire the x-ray images used to estimate the pose at each given time.